MEXICO CITY – Mexico City residents voted against the president's proposal to give private companies a bigger role in the country's state-run oil industry, according to results of a nonbinding referendum released Monday.

In the capital, more than 80 percent of those who voted Sunday opposed President Felipe Calderón's plan. Results were still being tallied in the other nine states that participated in the referendum organized by the leftist Democratic Revolutionary Party, or PRD.

About 820,000 Mexico City residents voted – a turnout of 11 percent, much lower than PRD officials had anticipated. The party said some 2 million people voted nationwide.

But the capital's PRD mayor, Marcelo Ebrard, nevertheless called the results “an imperative mandate.”

Voters were asked whether Mexico should allow private companies to participate in oil exploration, refining and distribution.

The referendum does not directly affect Calderón's bill, which is already before the Senate.

The president says Mexico doesn't have the expertise or funding needed to explore deep-water oil reserves, and allowing greater private partnerships would help declining output at the country's current oil fields. Experts say Mexico's proven reserves would last only 10 more years.

Opponents counter that the move is an attempt to privatize Mexico's oil industry, which was brought under government control in 1938 and remains a point of national pride. Mexico's Constitution says all oil belongs to the state and forbids giving concessions to private or foreign companies.

State oil company Petroleos Mexicanos, or Pemex, has been subcontracting some work to private firms for years. Calderón's proposal would expand that role in areas like exploration and refining.